Evaluation of Commercial Prototype Bacteriophage Intervention Designed for Reducing O157 and Non-O157 Shiga-Toxigenic Escherichia coli (STEC) on Beef Cattle Hide

Microbiological safety of beef products can be protected by application of antimicrobial interventions throughout the beef chain. This study evaluated a commercial prototype antimicrobial intervention comprised of lytic bacteriophages formulated to reduce O157 and non-O157 Shiga-toxigenic Escherichia coli (STEC) on beef cattle hide pieces, simulating commercial pre-harvest hide decontamination. STEC reduction in vitro by individual and cocktailed phages was determined by efficiency of plating (EOP). Following STEC inoculation onto hide pieces, the phage intervention was applied and hide pieces were analyzed to quantify reductions in STEC counts. Phage intervention treatment resulted in 0.4 to 0.7 log10 CFU/cm² (p < 0.01) E. coli O157, O121, and O103 reduction. Conversely, E. coli O111 and O45 did not show any significant reduction after application of bacteriophage intervention (p > 0.05). Multiplicity of infection (MOI) evaluation indicated E. coli O157 and O121 isolates required the fewest numbers of phages per host cell to produce host lysis. STEC-attacking phages may be applied to assist in preventing STEC transmission to beef products.

Application of Surfactant Micelle-Entrapped Eugenol for Prevention of Growth of the Shiga Toxin-Producing Escherichia coli in Ground Beef

Beef safety may be compromised by O157 and non-O157 Shiga toxin-producing Escherichia coli (STEC) contamination. The capacity of surfactant micelles loaded with the plant-derived antimicrobial eugenol to reduce STEC on beef trimmings that were later ground and refrigerated for five days at 5 ± 1 °C was tested to determine their utility for beef safety protection. STEC-inoculated trimmings were treated with free eugenol, micelle-encapsulated eugenol, 2% lactic acid (55 °C), sterile distilled water (25 °C), or left untreated (control). Following treatment, trimmings were coarse-ground and stored aerobically at 5 ± 1 °C. Ground beef was then sampled for STEC immediately post-grinding, and again at three and five days of storage. STEC minimum inhibitory concentrations (MICs) in liquid medium for free eugenol and 1% sodium dodecyl sulfate (SDS)-loaded micelles were 0.5% and 0.125%, respectively. STEC numbers on beef trimmings treated by sterile water (6.5 log10 CFU/g), free eugenol (6.5 log10 CFU/g), micelle-loaded eugenol (6.4 log10 CFU/g), and lactic acid (6.4 log10 CFU/g) did not differ compared to untreated controls (6.6 log10 CFU/g) (p = 0.982). Conversely, STEC were significantly reduced by refrigerated storage (0.2 and 0.3 log10 CFU/g at three and five days of storage, respectively) (p = 0.014). Antimicrobial treatments did not significantly decontaminate ground beef, indicating their low utility for beef safety protection.

Processing interventions for enhanced microbiological safety of beef carcasses and beef products: A review

Chilled beef is inevitably contaminated with microorganisms, starting from the very beginning of the slaughter line. A lot of studies have aimed to improve meat safety and extend the shelf life of chilled beef, of which some have focused on improving the decontamination effects using traditional decontamination interventions, and others have investigated newer technologies and methods, that offer greater energy efficiency, lower environmental impacts, and better assurances for the decontamination of beef carcasses and cuts. To inform industry, there is an urgent need to review these interventions, analyze the merits and demerits of each technology, and provide insight into 'best practice' to preserve microbial safety and beef quality. In this review, the strategies and procedures used to inhibit the growth of microorganisms on beef, from slaughter to storage, have been critiqued. Critical aspects, where there is a lack of data, have been highlighted to help guide future research. It is also acknowledge that different intervention programs for microbiological safety have different applications, dependent on the initial microbial load, the type of infrastructures, and different stages of beef processing.

Lactic Acid Resistance and Population Structure of Escherichia coli from Meat Processing Environment

To explore the effect of beef processing on Escherichia coli populations in relation to lactic acid resistance, this study investigated the links among acid response, phylogenetic structure, genome diversity, and genotypes associated with acid resistance of meat plant E. coli. Generic E. coli isolates (n = 700) were from carcasses, fabrication equipment, and beef products. Acid treatment was carried out in Luria-Bertani broth containing 5.5% lactic acid (pH 2.9). Log reductions of E. coli ranged from <0.5 to >5 log CFU/mL (median: 1.37 log). No difference in lactic acid resistance was observed between E. coli populations recovered before and after a processing step or antimicrobial interventions. E. coli from the preintervention carcasses were slightly more resistant than E. coli isolated from equipment, differing by <0.5 log unit. Acid-resistant E. coli (log reduction <1, n = 45) had a higher prevalence of genes related to energy metabolism (ydj, xap, ato) and oxidative stress (fec, ymjC) than the less resistant E. coli (log reduction >1, n = 133). The ydj and ato operons were abundant in E. coli from preintervention carcasses. In contrast, fec genes were abundant in E. coli from equipment surfaces. The preintervention E. coli contained phylogroups A and B1 in relatively equal proportions. Phylogroup B1 predominated (95%) in the population from equipment. Of note, E. coli collected after sanitation shared either the antigens of O8 or H21. Additionally, genome diversity decreased after chilling and equipment sanitation. Overall, beef processing did not select for E. coli resistant to lactic acid but shaped the population structure. IMPORTANCE Antimicrobial interventions have significantly reduced the microbial loads on carcasses/meat products; however, the wide use of chemical and physical biocides has raised concerns over their potential for selecting resistant populations in the beef processing environment. Phenotyping of acid resistance and whole-genome analysis described in this study demonstrated beef processing practices led to differences in acid resistance, genotype, and population structure between carcass- and equipment-associated E. coli but did not select for the acid-resistant population. Results indicate that genes coding for the metabolism of long-chain sugar acids (ydj) and short-chain fatty acids (ato) were more prevalent in carcass-associated than equipment-associated E. coli. These results suggest E. coli from carcasses and equipment surfaces have been exposed to different selective pressures. The findings improve our understanding of the microbial ecology of E. coli in food processing environments and in general.